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- Malduin
- A northern tributary to Taeglin.
- Mering Stream
- The border river of Rohan and Gondor. The Mering Stream or in (Sindarin) Glanhír formed the border between the Gondorian province of Anórien and the Rohan province of Eastfold. It flowed through the Firien Wood, which grows about the hill of Halifirien.
- Mindeb
- A northern tributary of Sirion. It began in the Ered Gorgoroth near the Pass of Anach, and was met by an unnamed tributary coming from the Crissaegrim. It formed the boundary between Dimbar and Nan Dungortheb.
- It formed the western border of the forest of Neldoreth in Doriath and was part of the Girdle of Melian. It is mentioned in Quenta Silmarillion chapter 14.
- Mitheithel
- A great river of Eriador, translated as Hoarwell in Westron. The source lay in northern Misty Mountains, from where the river sped through the Ettenmoors to bend south after them. The East Road crossed it at the Last Bridge, after which it was met by the Bruinen, forming the Angle. From there Mitheithel formed the northern border of Eregion, until came to the Swanfleet, where Glanduin flowed, and became the Gwathló (Greyflood) river.
- Morgulduin
- (S. 'river of sorcery') A river of Gondor that began at Cirith Ungol. It flowed past Minas Morgul towards Anduin, and was followed by the old Númenórean road from Osgiliath to Minas Morgul. It was crossed by the Harad Road with a bridge at the Crossroads.
- Morthond
- A river of Gondor beginning at the southern edges of the Dwimorberg at the end of the Paths of the Dead in the White Mountains. It then flowed past the ancient fortress of Erech and the Pinnath Gelin. After meeting its tributary Ringló it entered the Sea at Edhellond. Also translated as Blackroot.
Read more about this topic: List Of Middle-earth Rivers